1. Field of the Invention
The subject tower press filtering system is generally directed to a system for filtering solid particulates from a liquid. More specifically, the tower press filter system is directed to a system for extracting and compacting the solids from a substance having both solid and liquid components such as industrial slurry products, by-products, and the like. In chemical, mining, and other applications, both industrial and non-industrial, it is often desirable to separate as completely as possible the solid and liquid components of a given slurry material. The end product desired may, depending on the particular application intended, be the resulting liquid filtrate, the extracted solid particulates, or both. In any event, the filtering process is aided by a compression step whereby the solid particulates initially extracted by a filter medium from the filtrate are compacted to essentially squeeze out any remaining liquid. The resulting cake of solid particulates is washed, dried, then removed from the filtering system.
Such a filtering process is typically carried out in the art within a tower press filtering system having a plurality of displaceably stacked filter plates between adjacent ones of which an endless loop filter medium is routed. The stacked filter plates are clamped together and pulled apart by a clamping mechanism that actuates accordingly the displacement of a press plate coupled to the stack. The system typically operates as follows. The stacked filter plates are clamped together in sealed manner such that a chamber is formed above a span of the filter medium between adjacent filter plates. The material to be filtered is then fed into the chambers thus formed, and an initial filtering process occurs whereby filtrate within each chamber passes through the given span of filter medium and drains via the filter plate therebeneath. A compression process is next effected by suitable means known in the art, such as an expandable diaphragm in each chamber controlled by hydraulic pressurization, to compact the solid particulates collected on the filter medium in the chambers into cakes. After sufficient progression of this process, each diaphragm or other compression means employed, is depressurized to remove the compacting force from the resulting cakes, and a pressurized washing liquid is introduced into and through each chamber to wash away any unwanted liquids, salts, or other impurities. Each diaphragm is pressurized once more thereafter to squeeze the washing liquid out from the solid cakes. Finally, each diaphragm is again depressurized, and high pressure air is passed through the chambers to thoroughly dry the cakes remaining therein.
These steps form but one cycle of a filtering process. Upon formation of a solid cake as described, the clamping mechanism draws the filter plates apart, and a drive mechanism advances the loop of filter medium, causing discharge of the formed cakes from the filter plates. The filtering cycle is then repeated with each span of filter medium having advanced to the next pair of adjacent filter plates, or to/through a washing basin/chamber.
This type of tower press filtering system operates continuously over substantial stretches of time in many industrial applications. The dimensions and weights of components in such a system are necessarily quite significant, as they must accommodate high pressure operation and yield high filtering capacity. The compacting diaphragm, for instance, is pressurized in an exemplary application at approximately 230 psi, requiring the surrounding filter plates to be formed from steel, dense plastic, or other such heavy duty material of comparable strength and rigidity. Each filter plate is formed from such material to encompass, on average, five to ten square feet of filtering chamber area and a sufficient number of filter plates are employed in a given tower press to obtain 300-400 square feet of cumulative filtration area. This makes for a great number of very heavy filter plates, the precise, cyclic movement of which, over even a short period of time, becomes quite a challenge. Yet, highly precise and highly synchronized movement of such filter stacks is essential to productive operation of the system.
Without a sufficient degree of precision and synchronization, the coordinated coupling of adjacent filter plates--hence, the formation of adequate seals necessary for proper operation--may be compromised. Also, the consistency and uniformity of the compacting pressure applied to the solid particulates collected within given filtering chambers that is necessary for efficient formation of a consistently dry cake may be significantly disrupted, as may the level transport of the cakes on the advancing filter medium that is necessary to avoid premature or misdirected discharge thereof. Consequently, there is generally a need for appropriate measures by which the movement of components in a tower press filtering system is maintained in highly precise and synchronized manner.
In light of the continual movement of components having great bulk and weight in many tower press filtering systems, it is important that the means by which an air/liquid injection port is coupled to the feed ports/passages in the stacked filter plates are coupled in sealed manner to an air/liquid conduit be characterized by a sufficient degree of resilience. This resilience must be of sufficient nature and degree to withstand both vertical and lateral displacement deviations which invariably occur as the bulky, heavy filter plates are caused to move, stop, and periodically abut one another. Factor in the fact that in many industrial applications of tower press filtering systems, the material to be filtered is highly corrosive or otherwise noxious, it is also important that the resilience be accompanied by great durability. This is quite important to the actual utility, in practice, of a given tower press filtering system.
Another consideration of great practical importance is the configurability of the given filtering system. With its heavy duty construction and durable yet precise mechanization necessary in spite of that heavy duty construction, a tower press filtering system invariably represents a substantial capital investment. Hence, it is not feasible, much less prudent, to simply replace a given tower press filtering system with another of different configuration where, for instance, space or operational constraints restrict the stacked filter plates in the system on hand to a different number or to those having different dimensions. Convenient means whereby the system could be readily adapted to the insert, removal, or replacement of one or more filter plates would be highly desirable in such cases.
2. PRIOR ART
Tower press filtering systems which carry out the basic operational cycle described in preceding paragraphs are known in the art. In those known systems, a plurality of filter plates are displaceably coupled to a frame assembly and clamped together or drawn apart by a suitable clamping mechanism--often, a pair of piston and cylinder assemblies situated on opposing sides of the prevailing filter plate stack. The piston and cylinder assemblies extend from a support plate to a press plate between which the filter plate stack is disposed. The contraction of the piston and cylinder assemblies cooperatively draw the press plate toward the support plate until the press plate `closes` the stacked filter plates by clamping them together against the support plate. Conversely, the expansion of the piston and cylinder assemblies draws the press plate away from the support plate to thereby pull the stacked filter plates sufficiently apart to allow free advancement of the filter medium passed therebetween.
Each filter plate is formed with a substantially planar top surface which serves as the underlying support for the section of filter medium extending across it. Beneath this upper surface is defined a recess for receiving the material to be filtered. Each filter plate also includes a pair of manifold sections, usually located at the planar periphery of the filter plate. The manifold sections respectively define vertically extended conduit sections--one conduit section whose inner passage communicates with the given filter plate's inner recess through an inlet port formed therebetween, and the other conduit section communicating with drainage passages suitably formed to extend from the given filter plate's top support surface to collect and drain the flow of filtrate and other liquids passing through the filter medium section immediately above the top surface.
During operation of the system, a filtering cycle is initiated by the closing of the filter plate stack. A plurality of filtering chambers are then formed between adjacent filter plates when the top plate of one filter plate (and the section of filter medium passing across it) abuts the filter plate situated immediately above it to cover that plate's inner recess. Typically, the filter plates are dimensioned such that a filter chamber having a height dimension on the order of approximately two inches is formed between adjacent plates. The respective manifold sections of the stacked filter plates are, at this point, coupled together in sealed manner to define an inlet distribution conduit and a multi-access drainage conduit.
A slurry or other material to be filtered is then fed through the inlet distribution conduit until each of the filtering chambers between the stack of filter plates are filled. Solid particulates remain within those chambers while filtrate passes through the sections of filter medium lining the filtering chambers and drains to and through the drainage conduit. A compression process is then carried out within each of the filtering chambers to compact the solid particulates, squeezing out the remaining liquids. Various means are employed in the art for this compression process. An oft-employed means, however, is the provision of a liquid-impermeable membrane lining the surface of a given filter plate that substantially defines its inner recess. Thus situated, the membrane extends across the plane overlying the given filtering chamber.
In an exemplary system, such membrane in each filtering chamber is expanded by hydraulic means to serve as a pressurized diaphragm that exerts a downward pressing force on the solid particulates collected within that chamber. What then results within each chamber is a cake of solid particulates.
Often it is desirable to subject the cakes thus formed to a washing process to remove any salts or other impurities therefrom. Where this is the case, the compression force is removed from each cake by, for instance, depressurizing the membranes. A washing liquid is then pumped via the inlet distribution conduit to essentially rinse the cakes within their respective filtering chambers. Next, another compression step is performed as before whereby excess rinsing liquid remaining about and within the cakes is squeezed out. Finally, after the compression force is again removed, a drying step is carried out by introducing a high pressure flow of air or other gaseous stream through the filtering chambers, via the inlet distribution conduit.
The cakes are thereafter ready for discharge; and, the clamping cylinder assemblies are expanded to draw the filter plates apart. A drive mechanism then advances the filter medium by a predetermined length, the cakes being transported on the filter medium and discharged therefrom as the filter medium segments transporting them pivot about supporting roller structures. The cakes having been discharged from the filter medium in this manner, the drive mechanism is deactivated for the commencement of another filtering cycle.